This invention pertains to bulk storage bins, such as are commonly used to store bulk materials such as coal, ores, grain, coke and cement, for example. The invention further pertains to other bulk storage means, and methods and apparatus for recovering (or “reclaiming” bulk materials from such bulk storage means. Such bulk storage bins (and other bulk storage means) can be located on a ground site, or in the hold of a ship, for example.
There is a multitude of prior art for the storage of free-flowing bulk materials including principally: (1) bins, (2) bunkers, (3) silos, (4) domes, (5) barns, (6) highwalls, and (7) open stockpiles. The following background discussion centers on these principal types of bulk storage means within the context of how the particular structure or means is constructed, how the structure or means is compartmentalized to accept a variety of bulk materials, and how the bulk materials are reclaimed from the structure or means.
Prior art methods and/or apparatus for storing bulk solids include the use of (1) bins, (2) bunkers, (3) silos, (4) domes, (5) barns, (6) highwalls, and (7) open stockpiles. Each such storage means will now be generally described, and well as methods and/or apparatus that are commonly used to remove (i.e., “reclaiming”) the bulk solid from the storage means.
Bins are typically steel and/or reinforced concrete rectangular or square holding vessels that are relatively short in height compared to their plan dimensions. Bins are typically emptied of their bulk materials by means of gravity feed through a single bin hopper and single gated discharge opening at the bottom center of the bin. Bins walls are typically constructed of steel panels or of straight, cast-in-place (or precast) reinforced concrete walls of a specified thickness. Hydrostatic material forces are typically taken in beam action horizontally between the four corners of the bin, the steel or concrete wall sections being appropriately stiffened with reinforcement and stiffener beams. To provide for a variety of bulk materials, multiple bins are typically constructed in a row to make use of a single, stationary (i.e., fixed-in-place) discharge conveyor which is located underneath the bins. Each discharge point has a designated mechanical means of actuating the reclaim gate to an “open” or “closed” position and, in most cases, to a degree in-between these extreme positions, to thereby effect a metering of the bulk material flow. There can also be a feeder (e.g., conveyor type, vibratory type, or auger type, among others) below the gate or hopper opening to affect a metered flow of material onto the reclaim conveyor, or into trucks or trains or other mediums of conveyance. Discharge or draw-points are typically spaced apart at intervals under a continuum bin structure.
Bunkers are similar to bins but are typically 3-sided instead of 4-sided, and are typically a retaining wall type structure, and are emptied of bulk material via a tunnel reclaim system under the bunker. Allowance for multiple bulk materials is made by constructing multiple bunkers. The reclaim systems typically used for bunkers are similar to those used for bins.
Silos are typically relatively tall steel or reinforced concrete cylinders cast or assembled as a separate unit, or within the context of a pack of closely spaced or integrally cast cylinders. Cast-in-place silos can be cast with jump-form or slip-form systems. Reclaim of the bulk solids from silos is typically achieved by funnel flow or mass flow in the silo based on the angle of a conical hopper at the base of the silo. Large diameter silos typically have multiple, in-line draw points. Each draw point is typically equipped in a similar fashion to those on the bins with flow metering devices, most typically including vibratory feeders or augers and/or actuatable gates.
Domes are constructed as a hemisphere (i.e., no material is stacked against the shell) or super-sphere (i.e., material can be stacked against the shell) structure, and can be raised somewhat on a cylindrical perimeter stem wall to increase the storage capacity for a given dome radius. Domes are typically shot-creted to an external or internal airform. Allowance is made for multiple bulk materials by stacking the materials in separate regions under the dome, or by constructing multiple domes (one dome for each material). Reclaim from domes is accomplished in a variety of ways including: (a) a reclaim tunnel and draw points; (b) a loader (e.g., a front loader) and a truck; (c) a mechanical reclaimer, such as rakes and augers, which operates inside the dome to move the material to the center of the dome where the material is discharged down onto a conveyor belt in a tunnel; or (d) a combination of two or more of the above.
Storage barns are typically long and wide, A-frame, steel trussed buildings. They are very much like a dome in that the bulk material sits in a pile(s) under the barn, typically on a concrete pad, and typically the material does not touch the roof surface. Barns are different from domes in that they are longitudinally oriented rather than radially oriented. Multiple bulk solids are handled in barns by designating specific regions or lengths of the pile(s) to a particular material. Reclaim from barns is typically performed With mechanical reclaimers, the most prevalent being the bucket type scraper, or augers which traverse the sloping faces of the piles, drawing the material down to a discharge conveyor that resides in a trench along the side(s) of the pile. Another means of reclaim is tunnel reclaim under the pile with a rotary plow which traverses the length of the pile, essentially digging the material from the bottom of the pile and depositing it on a discharge conveyor.
Highwalls are a truncated version of open stockpiles in that the percentage of live reclaim is increased by truncating, on one or more sides, the toe of a conical or long pile. Multiple bulk materials are accommodated by providing multiple highwall piles (one pile for each material). Reclaim is accomplished with loader and truck, or with reclaim tunnels with discrete draw points which are typically near the highwall to optimize the live reclaim potential.
Open stockpiles are formed with fixed or mobile cantilevered stackers or, in the case of coal and coke, with stacking tubes. Multiple bulk materials are accommodated with multiple open stockpiles. Reclaim is typically accomplished via reclaim tunnels with discrete, fixed draw points, but mechanical reclaimers such as rakes and bucket wheels are still prevalent.
While these prior art storage and reclaiming means are generally effective for the storing and reclaiming of bulk solids, they do have some drawbacks. In the first instance, the height of storage structures, such as bins as silos, is generally limited by the cost of construction. As a general rule-of-thumb, the taller the structure, the thicker the walls of the structure will need to be (in order to resist earthquake loads as well as to contain the static loads imposed by the weight of the material stored within the structure). Any storage structure of significant height (for example, 15 meters or more) will be constructed from concrete. While very tall concrete structures can be formed, the cost of forming such tall structures typically outweighs the financial benefit of providing the tall structure, such that it is not economical to build such structures.
Secondly, each of the prior art bulk storage means described above allows, in one way or another, for multiple bulk materials to be stored. However, in most instances (with the exception of open stockpiles, for example) each of the prior art storage means do not provide flexibility with respect to accommodating the storage of multiple bulk materials. For example, a gang of eight discrete silos can store up to eight different bulk materials. However, if only two different bulk materials are to be stored in an 8-silo structure (in equal portions), then four silos must be dedicated to each material. In this instance, reclaiming one of the bulk materials requires unloading four separate silos. Generally, it takes longer to unload four silos of a first size than to unload a single silo that is four times as large as the first size.
As indicated above, it is desirable to provide a bulk storage bin or silo with the capacity for “live” reclaiming. That is, “live” reclaiming allows essentially all of the bulk material stored in the bin or silo to be unloaded, such that there is no material left in a “dead” zone within the bin or silo. For very large storage bins live reclaiming is achieved by providing a number of metered gates along the bottom of the bin, as also described above. When the bottom of a storage bin is an extended “V” shaped bottom, then live reclaiming generally requires that the bulk material be unloaded at every point along the V-shaped bottom. This requires a significant number of metered gates to accomplish, thus increasing the cost of the reclaiming system. As an alternative, the bottom of the bin can be formed as several in-line conical bottoms, such that a metered gate is only required for each conical bottom. However, this latter arrangement reduces the storage volume of the bin over a continuous V-shaped bottom configuration.
What is needed then is methods and apparatus for storing bulk materials, and methods and apparatus for reclaiming bulk materials from a bulk material storage means, which achieve the benefits accorded by such prior art methods and apparatus, but which avoid the detriments variously associated therewith.